The closed loop gain you computed for the non-inverting opamp configuration of 7.91 is correct.

The book's answer of 4 Vp-p would be more consistent with a closed loop gain of 7. It is as though the answer in the book failed to take into account the need to add 1 to the ratio of Rf/Ri when computing the gain of the non-inverting opamp stage.

It is possible that the book's answer was derived based on an inverting opamp stage. In that case the gain would be -Rf/Ri. Since the problem was to find the magnitude of the input that would result in the clipping condition then the negative sign would be of no concern.